This invention relates generally to sewage grinder pumps and more particularly to two-stage high head low flow sewage grinder pumps.
Many residential sewer systems use only the force of gravity to provide for discharging its wastewater into progressively larger sewer mains and ultimately to a dedicated treatment plant that is usually located in a low-lying area such that gravity can assist the flow of sewage. However, in a hilly land area, in a below-grade setting, along long horizontal pipe runs or perhaps due to smaller-diameter piping restrictions, gravity often will not suffice. In such situations, a lift-station or a stand-alone sewage ejector pump is required if gravity alone will not allow flow of sewage at a speed of at least 2 feet per second, which is considered to be a minimum required velocity to maintain suspended sewage solids in suspension. One type of ejector pump is a submersible grinder pump. In areas of flow pressure, one can employ such a fixture to move the sewage from a given location to a sewage collection system. The pump may be installed below the nearest available sewer line. The pump will either lift the waste to the level of the main drain or move the sewage through the piping.
Grinder pumps cut and grind solid materials into tiny pieces and are designed to reduce sewage particulate to a slurry. This overcomes sewage passageways restrictions and allows free movement of the fluid. A commonly used submersible grinder pump is a centrifugal pump with a recessed vortex impeller. In these systems, one can expect a power range of 2 to 7.5 horsepower (HP). Residences generally use the 2 HP models, principally due to its compatibility with typical residential electric-circuit configurations that provide comparatively low power. However, one may require a larger HP centrifugal pump, an intermediate lift station, or a progressing cavity style pump when sewer system pressures or flow resistance exceeds the capabilities of a 2 HP centrifugal pump. In residential applications, such systems are often unaffordable.
The progressing cavity pump's major advantage is its ability to work under relatively high pressures and allow service to areas with high-pressure requirements without the need for additional lift stations or relatively high HP pumps. Unfortunately, wear items that readily fail at high pressures, such as that pump's wobble stator arrangement, are a significant disadvantage.
Alternatively, centrifugal pumps offer higher flow rates than progressing cavity style pumps, have the ability to handle abrasives and slurries, and can operate at stall head or zero flow for extended periods without causing pump damage. For example, design pressures can be readily exceeded and can remain high until an upset condition, such as excessive simultaneous operations following a power outage, or high infiltration caused by poor installation, is resolved. However, a 2 HP residential centrifugal pump will have a significantly lower pressure limitation than a progressing cavity pump and is not suited for pressure sewer systems that achieve a total system head (distance pump is capable of lifting fluid) greater than 120 feet at the pump.
Thus, in a pressure sewer system where upset conditions produce high system pressures, both the progressing cavity and typical single-stage centrifugal grinder pumps lack relevant design efficiencies and possess limiting capabilities. However, since the centrifugal pump with recessed vortex impeller is more robust and reliable, a welcome pump design modification will combine this advantage with the high-pressure advantage of the progressing cavity pump to produce a pump that is affordable and still suitable to residential applications.
The foregoing illustrates limitations known to exist in present sewage grinder pumps. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.